A full-automatic military weapon, as long as its trigger or other control is held down, will continue to load and fire until it is out of ammunition, it fails, or the trigger is released. This contrasts to a semi-automatic weapon, which will load and fire once for each pull of the trigger.
Some weapons have a "burst" mode where several rounds, typically three, will be fired for each pull of the trigger. Burst mode is a compromise between the greater hit probability of several bullets, and wasting ammunition. Especially when hand-held, it is very difficult to control a full-automatic weapon when firing many rounds; experienced users fire bursts anyway. If someone actually tried to fire, for long bursts, some of the heavy machine guns featured in action movies, any real human being would soon find himself or herself seated on the ground, firing straight up.